Modified 2D van-der-Waals materials for advanced bio-applications

2D materials such as graphene and hexagonal boron nitride (h-BN) have excellent functional properties for applications in information and communication, and medical technology. h-BN has been intensively studied for its characteristics as the only electrical insulator in the 2D family, with a crystal structure resembling that of graphene. The properties of h-BN can be tuned by doping, functionalization, and hybridization of the h-BN layers. The potential of tuning the properties leads to a broad range of possible applications, e.g., in electronics, optoelectronics, as sensors and as insulating layers. h-BN-based materials are biocompatible, and they can hence be used for biomedical applications. In the BORNIT-project (Modified 2D van-der-Waals materials for advanced bio-applications), we have performed experimental and theoretical studies of h-BN and defect structured h-BN thin films. We have studied the role the choice of substrate on the BN-material and corresponding functional properties. We have used a pulsed laser deposition (PLD) and sputtering laboratory established at NTNU and we have developed routines to prepare h-BN films on different types of substrates (highly ordered pyrolytic graphite (HOPG) as well as low cost and flexible copper and nickel foils). PLD gave good control of the film thickness and stoichiometric transfer of the ablated material. We have systematically studied the films by in situ high-pressure reflection high-electron diffraction, atomic force microscope, Raman spectroscopy and X-ray photoelectron spectroscopy. We have further assessed the coupling between defect chemistry, adatom adsorption, and functional properties in h-BN films using density functional theory (DFT) calculations. We have found that the type of substrate affects the defect chemistry and corresponding functional properties in PLD deposited h-BN films. We have shown that adsorption of transition metal adatoms on the surface strongly depends on the choice of substrate and corresponding defect chemistry, which, in turn, determines the possibility for growth of nanoparticles at the surface. Our theoretical findings provide new fundamental insight into the coupling between defect chemistry, surface chemistry, and functional properties in materials, which is key for designing new materials with controlled new functionalities in the future. The theoretical modelling has been performed in collaboration with Aristotle University of Thessaloniki, Greece. The work on h-BN has been supplemented with studies of thin film and clusters of oxide systems to gain a broader insight into the defects of these materials and how they influence on functional properties. Advanced transmission electron microscopy (TEM) techniques have been utilized to gain fundamental understanding of the materials. The PhD candidate has gained valuable experience in advanced TEM techniques that can be used in a variety of research fields for her future career. The project has resulted in 12 scientific publications whereof 3 were published after the end of the project and at 8 international scientific conferences.

The main outcome of the BORNIT-project is the establishment of a multidisciplinary knowledge covering 2D-nanostructured materials and thin films, advanced structural characterization with transmission electron microscopy as the main tool, combined with atomistic modelling. New methodology for thin film deposition of 2D materials has been developed. The combined experimental and modelling approach has contributed to a thorough understanding of the effect of the type of substrate for the film properties and the influence of defects on the materials properties. Well trained PhD candidate and two post docs within the filed of nanomaterials synthesis and characterization will contribute to scientific development through their gained knowledge in their future positions. The learning from the BORNIT-project activities will be brought forward to impact the work in the FACET (Functional materials and materials chemistry) research group in future projects.

The field of nanotechnology applied to medicine (nanomedicine) is developing at a fast pace and is expected to provide solutions for early diagnosis, targeted therapy, and personalized medicine. In this context, multimodal contrast agents based on nanostructures that combine magnetic and optical intrinsic responses can offer improvements in patient care and at the same time can reduce costs, contribute to the efficiency of the hospital logistics, and enhance safety by limiting the number of contrast agent administrations required for imaging purposes. The aim of the present project is to develop a new generation of multimodal contrast agent, based on 2D-hBN nanostructures, for magnetic and photonic based bio-imaging. For this purpose, 2D-hBN will be deposited by PLD technique and further modified. This modification consists of in-situ hybridization of 2D-hBN nanostructures by implanting energetic charged atomic-nanoclusters of plasmonic materials. This shallow implantation will lead to Localized Surface Plasmon Resonance (LSPR) response. The exposure of 2D-hBN to implantation will result in the formation of controlled vacancy defects, favoring the spontaneous spin polarization and the formation of a local magnetic moment. In addition, 2D-hBN materials can host the created defects whose electronic states lie deep within their large bandgap, inducing single quantum emitters behavior. The resulting nanostructures, with intrinsic magnetic, Quantum Dots emitters, and plasmonic responses, promise breakthrough advances in multimodal bio-imaging and single molecule sensing. These nanostructures will improve the safety of the patient as they are transition-metal-free with intrinsic photonic response.